Optical communication between electronic systems and/or subsystems (collectively "assemblies") is well known. See, for instance, U.S. Pat. No. 4,533,833. Conventionally, an electrical output from a first assembly (e.g., a circuit board) is used to modulate the optical output of a LED or laser, and the modulated output is detected by appropriate means (e.g., a PIN photodetector) on a second assembly, with the electrical output of the detector providing an input for the second assembly.
It has previously been proposed (Journal of Applied Physics, Vol. 51(4), pp. 1919-1921) that photodiodes and a particular semiconductor laser ("trap-doped" laser) could be interconnected to provide, in one configuration, the logic AND function, and in another configuration, the logic OR function. A laser having two (or more) independently addressable "loss" sections is disclosed in co-assigned U.S. patent application Ser. No. 407,608, filed Sep. 9, 1989 for K. Berthold et al. This laser can serve as a logic element that has electrical inputs and an optical output. The laser can, for instance, provide the logic AND function.
Co-assigned U.S. patent application Ser. No. 07/601,477, filed Oct. 19, 1990 for S. Luryi (incorporated herein by reference) discloses a real-space-transfer light emitting device that can be embodied in a logic element that has electrical inputs and an optical output. The device can provide novel and useful functions. For instance, depending on the input to a control terminal the device can provide logic OR or logic NAND. Logic elements that have electrical inputs and an optical output will herein be referred to as "electro-optical" (E/O) logic elements.
E/O logic elements are expected to find use in a variety of applications, e.g., in optical communications or data processing. In general, articles or systems that utilize logic elements will contain a multiplicity of such elements, with the input of one or more of the elements being responsive to the output of another of the elements. One or more of the logic elements can be a E/O logic element. Such articles or systems desirably would contain features that facilitate communication between an E/O logic element and another logic element (including another E/O logic element). Desirably such features are simple and inexpensive, and do not introduce significant time delay. This application discloses such features, and apparatus that comprises a E/O logic element that is optically interconnected with another logic element.